<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <style type="text/css">
        #titleName {
            color: red;
        }
        /* 层叠式体现 */
        p {
            font-size: 50px;
        }
    </style>
    <title>Document</title>
</head>
<body>
    <p id="titleName">id选择器</p>
</body>
</html>